Solar energy is a clean, environmentally friendly energy source. People have long been committed to its development and use. Especially in recent years, due to the rising oil price, increasing requirements for environmental protection and restraint of atmospheric carbon dioxide emissions, various countries have taken more efforts to carry out study on the utilization of solar energy, and especially put more efforts on how to obtain and utilize solar energy more efficiently.
Solar photo-thermal power generation is one of the most economical means to achieve high power generation in replacement of conventional energy sources. The respective advantage and disadvantage of three types of solar photo-thermal power generation is very obvious, for example, the tower type is of high efficiency, but at vast one-time expense; the trough type is of low cost, but with low efficiency relative to the tower type and the dish type; a stand-alone device of dish type can achieve standardized production, but the scale is difficult to expand.
Concentrating photovoltaic (CPV) refers to a technology directly converting the converged sunlight into electrical energy by photovoltaic cells with high conversion efficiency. Concentrating photovoltaic is also a choice to realize low cost solar power generation. Fresnel array scheme is one of the light concentrating methods.
A linear Fresnel solar light concentrating device primarily includes a linear Fresnel reflector strip system and a receiving unit. The linear Fresnel reflector strip system includes a linear reflector strip field. The linear reflector strip field is composed of a plurality of reflector strips disposed in parallel side by side, and the reflector strips, driven by a tracking unit, can track the movement of the sun, which ensures the incident light being reflected to the receiving unit continuously. The sunlight reflected by these reflector strips is concentrated toward the receiving unit disposed above these reflector strips, and the solar power is converted into thermal or electrical energy through the receiving unit. One receiving unit is usually disposed over a plurality of reflector strips to receive the sunlight reflected by the plurality of reflector strips.
In current linear Fresnel solar light concentrating systems, the Fresnel reflector field is arranged in a horizontal line and close to the basic plane such as the ground, which brings some inconvenient factors: 1. usually there is more dust contamination close to the ground; 2. the dust on the surface of the reflector strips of the Fresnel reflector field thickens after certain period, which severely reduces the reflectivity of the reflector strips and requires regular cleaning in a relatively short cycle, and meanwhile it is inconvenient for an operator to clean due to the compact arrangement of the Fresnel reflector field disposed above the ground, and operations can be done only by rotating the reflector strips to a vertical position and the operator enters from the gap between the reflector strips to operate, thus the width of the reflector strips must be very wide, e.g. 2 meters, so that there will be enough width for repair (the space for repair is about 2 m); the width of the reflector strips is of relatively large size, so the strength required needs to be enhanced and, thus, the cost can hardly be reduced; 3. the reflector strips are typically flat plate reflectors, which facilitates manufacturing, but tracking accuracy cannot be guaranteed, and the reception width of the receiving unit is greater than the width of the flat plate reflector strips; in order to obtain symmetrical arrangement of the Fresnel reflector field and less end loss effect (the converged light is heavily slanted from the axis of the receiver), the current reflector field generally adopts north-south layout, so the required tracking range is wide, e.g., plus or minus 80 degrees, thus, the tolerance rate of the reflector strips in the reflector field, especially those on edge of the reflector field, is very small (or the desired width of the receiving unit is very wide), and the receiving unit is arranged such that the height of the receiving unit which exceeds the field plane is smaller than half of the field width of the present group of fields, usually a quarter of the field width of the present group of fields; to obtain a higher concentrating multiple and a better tolerance rate and reduced cost, the width of the reflector filed is very wide and the number of the axes of reflector strips is large, which is of high cost and poor reliability; 4. the reflector field is arranged in a horizontal line, during the tracking process, the shading rate between the reflector strips especially the reflector strips on edge of each column of the reflector field is severe (the back of the front reflector strip occludes the light reflected by the back reflector strip), thereby reducing light concentration efficiency of the reflector strips; 5. the reflector field is directly arranged on the ground, occupying large areas, and the land utilization is not high, which is a waste of land resources; 6. the problem of low thermal efficiency resulted from low light concentrating multiple (the ratio of the total light reception width of the reflector strips to the width or diameter of the absorber tube under the condition of perpendicular incidence of the sunlight is about 30˜60 times) is prevalent.
Therefore, how to improve light concentrating multiple, light concentration efficiency and reliability of the Fresnel reflector fields, overcome the inconvenience in repair and maintenance, reduce construction costs and improve land utilization, etc., has become a major issue in linear Fresnel light concentrating technology.